This invention relates to a needle assembly for implanting therapeutic elements. More specifically, this invention relates to such an assembly which allows the user to load and place radioactive xe2x80x9cseedsxe2x80x9d in the body for the purpose of treating cancer.
The placement of a pattern of radioactive sources in the body to treat cancer by destroying cancer cells with low dose radiation is an accepted and preferred method of treatment as an alternative to general surgery.
These radioactive sources or xe2x80x9cseedsxe2x80x9d are placed into the body using multiple hollow needles or needle assemblies. The needles act as holders and carriers of such seeds until the needles are inserted into predetermined areas of the body. Once the needles are positioned, the seeds are deployed from each hollow needle by a solid wire stylet to permanently reside in the body as the radioactive dose decays over the treatment time. As many as 25 or more needles are used in each procedure. Typically, a physicist must prepare the needles or cannula and load the seed sources and spacers into each cannula prior to the procedure. Bone wax has been used to close the end of the cannula. The wax is placed into the first 2-5 mm of the distal tip of the cannula to prevent the radioactive xe2x80x9cseedsxe2x80x9d from dislodging or falling out prior to insertion of the cannula into the body. The doctor then inserts the cannulas into the patient and deploys the seeds into the area to be treated.
Prior art needle assemblies disclose a cannula with a sharpened distal tip and an inner solid wire stylet that is used to push the radioactive seeds into the body. The proximal end of the cannula consists of a plastic or metal hub that allows the loading of the radioactive seeds into the cannula. The proximal end of the stylet is a plastic or metal handle for manipulation of the stylet.
The prior art devices are prepared for use by plugging the end of the cannula with bone wax. The bone wax extends into the first 2-5 mm of the distal tip of the cannula to contain the seeds and to prevent body fluids from entering the cannula before deployment of the seed. The bone-wax-plugged cannula is loaded with radioactive seeds held apart by short non-radioactive spacers that position the seeds in the body to achieve an even distribution of radiation to treat the suspected cancer in vivo.
Prior to insertion, the stylet is axially introduced into the proximal end of the cannula and rests upon the stack of seeds and spacers, which are held in place by the bone wax at the distal tip of the needle. Once the cannula is inserted into the body to the proper position, the stylet is held firm and the cannula is axially moved toward the proximal end of the stylet. This motion deposits the radioactive seeds and spacers into the body in a track or line of seeds as the cannula is pulled back.
There are two principal types of radioactive seeds. xe2x80x9cFreexe2x80x9d seeds are individual radioactive seeds that are loaded in the cannula with small cylindrical spacers stacked in between the radioactive seeds. The second type is a pre-manufactured xe2x80x9cstrandxe2x80x9d of radioactive seeds that are encapsulated in a biodegradable material that spaces the radioactive seeds apart from one another.
The complications involved in the prior art stem from the use of bone wax or other materials that are used to plug the cannulas prior to the loading of the radioactive seeds.
Bone wax has many drawbacks:
1. Bone wax cannot be applied into the distal end of the cannula in a manner which assures a consistent positioning of the first seed in the cannula. The amount of wax varies needle to needle.
2. Bone wax is sticky and difficult to apply.
3. Bone wax may cause the first few seeds being deployed to stick to the end of the cannula as it is being withdrawn, displacing them from their intended position in the treated tissue (adjacent the prostate, for instance).
4. If the seeds and spacers must be removed after initial loading to change the pattern of seeds and spacers in a given needle, the bone wax prevents the unloading of the seeds in contact with the wax. This prevents the needle from being able to be reused in the procedure.
The needle assembly of the invention comprises a needle which may be delivered to the user already loaded and sterile. This reduces preparation time as well as personal exposure to the radioactive seeds.
The needle assembly of the invention exactly locates the first seed a repeatable and known distance from the distal end of the cannula in each needle used thus improving the accuracy of placing the radioactive seeds in the body.
The positioning means for the first seed may take one of a variety of forms, all of them yieldable to permit the seed to be pushed past the distal end in the implantation.
The needle assembly of the invention may include a biocompatable end plug which may be made of a variety of materials including absorbable or non-absorbable suture materials either in a braided or monofilament configuration or molded biocompatable polymers. In one embodiment of the invention, the plug may be held in place by a mechanical detail proximal to the distal end of the cannula.
This detail may be formed by parallel slits in the body of the cannula, a xe2x80x9cUxe2x80x9d shaped cutout in the cannula creating a xe2x80x9ctonguexe2x80x9d that can be displaced into the interior of the cannula, or small holes that pierce the tubular body of the cannula leaving a web between the holes. In each instance the xe2x80x9cwebxe2x80x9d of needle material created by the hole or slitting process in the tubular body of the cannula allows for a predetermined sizing of the inner diameter of the cannula to hold the end plug or seeds in place prior to deploying them into the body.
In an alternate embodiment of the invention, holding the biocompatable end plug in place inside the cannula at the distal end of the cannula may be accomplished by modifying the diameter of the plug by mechanical distortion means or expanding the diameter of the plug by heating the material until it swells or exposing the plug to solvents.
By enlarging the diameter of the biocompatable end plug, there is created a tight fit between the plug and the cannula body at the distal tip.
The stylet of the inventive needle may be provided in a hollow tubular form. The tube used in the stylet extends through the stylet handle to create an air passageway. This hollow stylet is provided to prevent air pressure from building up inside of the cannula caused by the tight fit of the stylet and the interior diameter of the cannula. This build-up of air pressure may cause premature dislodging of the seed source as the stylet is introduced into the cannula after loading and prior to expulsion of the seeds in the body.
In the case of encapsulated seed sources, the hollow stylet can capture the tail end of the encapsulated strand and prevent the tail end from becoming entrapped between the inner diameter of the cannula and the outer diameter of the stylet during its deployment.
In essence, for implanting a therapeutic element, the invention is a needle assembly comprising a cannula having a sharpened distal end, a line of elements in the cannula extending rearward from the distal end and yeildable means for positioning the element more proximate the distal end a predetermined distance from the distal end. The assembly also includes a stylet reciprocable in the cannula and engaging the end of the line of elements more remote from the distal end of the cannula.